This invention relates to plug and receptacle connections for joining two fiber optic cables together for optical energy transmission from one to the other. More particularly, it relates to the provision of an alignment system comprising an alignment key on the plug and a key slot on the receptacle, in which the plug and the fiberoptics cable to which it is connected can be rotated in position relative to the key, the key slot and the other fiberoptics cable, until a desired rotational alignment of the two cables is achieved, and then the alignment key can be fixed in position on the plug so that in the future whenever it is inserted into the key slot the desired rotational alignment of the two cables is achieved.
When the ends of two optical cables are connected together, with their optical fibers in axial alignment, for optical energy transmission from one cable to the other, optimum results are obtained when the optical fibers of the two cables are in a particular position of rotational alignment. U.S. Pat. No. 5,181,267, granted Jan. 19, 1993, to Jeffrey T. Gerace, Alan E. Plotts and Frederick H. Abendeschein, and assigned to AMP Incorporated of Harrisburg, Pa., provides the plug component of a plug and receptacle connection with a ring mounted alignment key and provides the receptacle component with a key slot adapted to receive the alignment key. A girth groove is formed in a sidewall of the plug and a hexagonal collar is provided immediately rearwardly of the girth groove. The collar provides six flats at its periphery representing six positions of adjustment. The ring is positioned on the plug, forwardly of the girth groove. The alignment key is aligned with the key slot and then the plug and the cable to which the plug is connected are rotated relative to the ring, the alignment key, the key slot and the other optical cable. When a desired alignment is found, the plug is rotated to place the closest flat on the collar in a position to be engaged by the tab on the ring. Then, the ring is moved rearwardly into the girth groove, moving with it the tab and positioning the tab on the selected flat. The engagement of the tab and the flat holds the ring and the alignment key in a set position on the plug body. Thereafter, the plug and receptacle connection can be disconnected and then reconnected and when reconnected the alignment of the two cables is established by inserting the key into the key slot. A problem with this arrangement is that it only allows for six azimuthal positions of the key on the plug.
An object of the present invention is to provide a polarizing ring with an alignment key in which the ring can be positioned in an infinite number of azimuthal positions around the body of the plug.
The present invention includes providing a plug for an end of a fiberoptic cable with an elongated plug body that is characterized by an end portion having an outer end, a forward girth groove in said body spaced axially inwardly from said outer end, and a rearward girth groove in said body that is axially inwardly adjacent the forward girth groove. The rearward girth groove is deeper than the forward girth groove. A ring surrounds the plug body. The ring is sized to make a loose fit with the rearward girth groove and an interference fit with the forward girth groove. There is a key on the ring that projects axially forwardly from the ring onto the end portion of the plug body. The ring is initially positioned in the rearward groove so that the body can be rotated in position relative to the ring and key, for the purpose of aligning the optic fiber in the first fiberoptic cable with the optic fiber in a second fiberoptic cable to which the first cable is to be connected. After proper azimuthal alignment is achieved, the ring is pushed axially forwardly out from the rearward girth groove and into the forward girth groove. When the ring is in the forward girth groove, its interference fit with the forward girth groove holds the ring and the key fixed in position on the end portion of the plug body.
In preferred form, the ring is provided with a rear end against which a force can be applied for pushing the ring out from the rearward girth groove and into the forward girth groove. The rearward girth groove has a forward end wall and the ring has a forward end wall that is positioned to contact the forward end wall of the forward girth groove when the ring is pushed forwardly, so as stop further forward movement of the ring on the plug body.
In preferred form, a nut is mounted on the plug. The nut has a sidewall that surrounds the plug body and a forward end portion that surrounds the ring and the key. The forward end portion includes internal threads. In preferred form, the nut is provided with a radially inwardly directed internal flange, intermediate its ends. This flange has an inner diameter through which the plug body extends. Preferably, at least one annular bearing member surrounds the plug body at a location axially between the internal flange and the rear end of the ring. The plug body includes a lock ring rearwardly of the internal flange. The lock ring is positioned to make contact with the internal flange when the nut is moved rearwardly. This keeps the nut from moving rearwardly off of the plug body.
In preferred form, the plug includes a ferrule that projects axially forwardly from the plug body. The ferrule includes a longitudinal opening for receiving an optical fiber.
The invention also includes providing a connector for connecting confronting ends of first and second lengths of fiberoptic cable. The connector is characterized by a tubular receptacle adapted to be connected to an end of a first length of fiberoptic cable and a plug adapted to be connected to an end of the second length of fiber optic cable. The receptacle includes a sidewall defining a plug receiving socket opening. The sidewall includes an axial key slot. The plug is as previously described.
The ring on the plug is initially positioned in the rearward groove on the plug. The plug is then inserted into the socket and the key on the ring is placed in alignment with the axial key slot in the sidewall of the receptacle. Then, the connector body and the cable to which it is connected are rotated in position relative to the receptacle, the ring and the key, until the end of an optical fiber in the first length of fiberoptic cable is in a desired rotational position relative to the end of an optical fiber in the second length of fiberoptic cable. Then, the ring is forced axially forwardly out from the rearward girth groove and into the forward girth groove. When the ring is in the forward girth groove, its interference fit with the forward girth groove functions to hold the ring and the key fixed in position on the end portion of the plug body. Then, the plug can be detached from the receptacle during the normal course of things and can later be connected again to the receptacle and proper alignment of the two optical fibers will be reestablished by a simple axial movement of the key on the plug into the key slot in the sidewall of the receptacle.
In preferred form, a nut is mounted on the plug. The nut has a forward end portion that includes internal threads which mate with external threads on the sidewall of the receptacle. The nut includes a radially inwardly directed internal flange intermediate its ends. When the nut is rotated to thread it onto the receptacle, this flange exerts an axial force on the rear end of the ring, forcing the ring forwardly from the rearward girth groove into the forward girth groove. In preferred form, at least one annular bearing member surrounds the plug body at a location axially between the internal flange and rear end of the ring. The bearing member(s) transmits the axial movement of the flange into an axial force on the rear end of the ring.
Other objects, advantages and features of the invention will become apparent from the description of the best mode set forth below, from the drawings, from the claims and from the principles that are embodied in the specific structures that are illustrated and described.